(1) Field of the Invention
This invention relates to a system and method for detecting wafer shift/slide in a chamber. In particular, it determines whether there is a net resultant force that may cause an unconstrained wafer to move from its original position in a chamber by measuring the relative chamber vibrations in three orthogonal directions.
(2) Description of the Prior Art
In the manufacture of semiconductor devices, silicon wafers are processed in multiple chambers. These wafers are generally supported in the chambers by wafer support units which have little or no contact with the patterned surface of the wafers to reduce contact-induced defects. However, such wafer support units have a weaker grip on the wafers. As a result, wafers can easily be displaced from their original positions when the chambers experience perturbations or vibrations created by any moving parts, such as slit valve, cryo pump, exhaust pump, process motor and robot arm. Other external sources, including human-induced vibration such as equipment maintenance work and footfall activities, can also cause the wafer to shift.
It is important to detect wafer shift/slide within a chamber as soon as it occurs because a wafer that is not normally positioned could cause the following problems:                The wafer will not be correctly clamped by the robot arm out from the chamber.        The wafer will be bumped into fragments by the robot arm inserting into the chamber. As a result, the equipment will have to be stopped to clear the fragments. This will affect the normal operation in the production and shorten the lifetime of the elements of process tools.        The wafer will not have the full complement of the integrated circuits produced on it.        Some wafer fabrication equipment, like sputtering machine, consists of an electrode which must be completely covered by the wafer during processing. However, a misaligned wafer will not be able to do so. When the wafer surface is bombarded with plasma, some of the plasma unintentionally bombards the electrode which creates airborne contaminant particles that fall on the semiconductor dies and lowers production yield of the semiconductor circuits fabricated on the wafers.        
Therefore, a real-time system and method for detecting wafer shift/slide in a chamber will be highly advantageous.
Currently, there are a few known systems and methods for ensuring that wafers are in their nominal or intended positions. They include those disclosed in U.S. Pat. No. 5,483,138, U.S. Pat. No. 5,563,798, U.S. Pat. No. 5,740,062, U.S. Pat. No. 5,982,492, U.S. Pat. No. 6,298,282B1, U.S. Pat. No. 6,471,464B1, U.S. Pat. No. 6,576,483B1, U.S. Pat. No. 6,601,313B2, U.S. Pat. No. 6,778,266B2, U.S. Pat. No. 6,900,877B2, U.S. Pat. No. 6,934,661B2, U.S. Pat. No. 6,938,505B2, U.S. Pat. No. 7,029,930B2, U.S. Patent Publication No. 2004/0151574A1, U.S. Patent Publication No. 2005/0012938A1, U.S. Patent Publication No. 2006/0209307A1 and U.S. Patent Publication No. 2007/0140826A1.
U.S. Pat. No. 5,483,138 to Shmookler et al., U.S. Pat. No. 5,563,798 to Berken et al., U.S. Pat. No. 5,740,062 to Berken et al., U.S. Pat. No. 5,982,492 to Oppenheimer et al., U.S. Pat. No. 6,601,313B2 to Shin and Kim, U.S. Pat. No. 6,778,266B2 to Hu et al., U.S. Pat. No. 6,934,661B2 to Yuen et al., U.S. Patent Publication No. 2004/0151574A1 to Lu, U.S. Patent Publication No. 2005/0012938A1 to Chen and Wei and U.S. Patent Publication No. 2007/0140826A1 to Ho and Shieh use optical sensors to detect the position of wafers. U.S. Pat. No. 6,900,877B2 to Raaijmakers determines wafer drift by using one or more cameras to capture the image of wafers, while U.S. Pat. No. 6,938,505B2 to Chen et al. detects misaligned or broken wafers based on uneven load distribution on supporting pins.
In U.S. Pat. No. 6,298,282B1 to Guldi et al., a vibration sensor placed on at least one of the robotic arm or under the cassette control of the robotic arms detects excessive vibration to wafers during their transport in and out from a cassette.
In U.S. Pat. No. 7,029,930B2 to Tomer et al., an electronic recording system attached to a test wafer records the motion of wafers, and fine perturbations and vibrations in their motion during their progress through and between semiconductor process and inspection machines in the course of the actual manufacturing process or in test cycles of these machines.
U.S. Patent Publication No. 2006/0209307A1 to Sun-bong Kim discloses how defects are prevented from occurring during an exposure process by detecting vibration of and measuring the relative position of components of the exposure apparatus. The exposure apparatus includes an external frame on which a reference mirror is disposed, a projection lens, a first mirror fixed relative to the projection lens, a wafer stage, a second mirror fixed relative to the wafer stage, and an interferometer system that detects vibration of the projection lens using the reference mirror and the first mirror and detects the position of the wafer stage relative to the projection lens using the first and second mirrors. A second interferometer system may be provided to detect vibration of the first interferometer system.
U.S. Pat. No. 6,471,464B1 to Fay et al. discloses a device for orienting and/or centering a wafer. The device employs a CCD camera and backlighting source which enhances the CCD camera's ability to detect wafer position. The backlighting source may be positioned along the side of the wafer opposite the CCD camera, or may be positioned adjacent to the CCD camera. When positioned adjacent to the CCD camera, one or more shields are employed to prevent direct or reflected light from impacting the top surface of the wafer being detected by the CCD camera. Accordingly, the only light detected by the CCD camera is light which passes the wafer and reflects from a surface there beyond, back to the CCD camera, resulting in effective backlighting of the wafer. The image of the wafer may be further sharpened by roughening the surface from which light reflects back to CCD camera.
U.S. Pat. No. 6,576,483B1 to Chou et al. discloses a backside cannelure of an electrode to provide for detecting semiconductor wafer shift after the wafer has been positioned over the cannelure of the electrode. The wafer has a backside and a proper position over the cannelure. The cannelure exposes the backside of the wafer to a gas piped in through one or more holes of the electrode. The cannelure has a size such that deviation of the wafer from its proper position by more than a threshold partially exposes the cannelure, such that the gas leaks from the partially exposed cannelure. A gas flow detector may detect the gas leaking from the cannelure, and provide corresponding detection of the wafer deviating from its proper position.